1. Field of the Invention
The present invention relates to a toner and a developer, especially to a toner to which a crystalline polyester resin is added, which is excellent in fixing ability and which forms high-quality images, and to a developer containing the toner.
2. Description of the Related Art
In recent years, demand has arisen on the market for toners having various advantageous properties such as small particle diameters for forming high-quality output images and improved low-temperature fixing ability for energy saving.
Toners obtained by the conventional kneading-pulverizing method are not easily made to have a small particle diameter. In addition, their shape is amorphous and their particle size distribution is broad. Furthermore, these toners have various problems such as requiring a large amount of energy for being fixed.
In particular, when toner materials including wax (releasing agent) for improving fixing ability are used to produce a toner by the kneading-pulverizing method, cracks occur at the interfaces of the wax during pulverization, resulting in that the wax exists on the toner surface in a large amount. As a result, although the releasing effects can be obtained, toner adhesion to a carrier, a photoconductor and a blade is likely to occur. The properties of such toners are not satisfactory in total.
In order to overcome the above-described problems the kneading-pulverizing method has, there is proposed a method for producing a toner by the polymerization method.
According to the polymerization method, toners are made easily to have a small particle diameter. Their particle size distribution is sharper than that of the toners obtained by the pulverizing method. Furthermore, the wax can be embedded in the toner particles.
As one exemplary polymerization method, Japanese Patent Application Laid-Open (JP-A) No. 11-133665 discloses a production method for a toner having a practical sphericity of 0.90 to 1.00, using, as a binder, an elongated product of a urethane-modified polyester for the purposes of improving the fluidity, low-temperature fixing ability and hot offset resistance of toner.
Also, JP-A Nos. 2002-287400 and 2002-351143 and other patent literatures disclose a production method for a toner having excellent fluidity and transferability as powder with a small particle diameter as well as being excellent in heat resistant storage stability, low-temperature fixing ability and hot offset resistance.
Japanese Patent (JP-B) No. 2579150 and JP-A No. 2001-158819 disclose a toner production method including an aging step for producing a toner binder having a more uniform molecular weight distribution and for attaining both desired low-temperature fixing ability and desired offset resistance.
Moreover, there is disclosed a method in which a crystalline polyester is used in the polymerization method for improving low-temperature fixing ability. JP-A No. 08-176310 and other patent literatures disclose a preparation method for a dispersion liquid of a crystalline polyester using a solvent for phase separation. This method can prepare a dispersion liquid whose dispersoids have a particle diameter of several tens micrometers to several hundreds micrometers, but cannot prepare a dispersion liquid whose dispersoids have a volume average particle diameter of 1.0 μm or less applicable to a toner. Furthermore, JP-A No. 2005-15589 discloses an attempt to make smaller the dispersion diameter of a crystalline polyester by mixing the crystalline polyester only with a solvent and by increasing and decreasing the temperature of the mixture. However, the particle diameter of the crystalline polyester obtained by this method is not uniform nor satisfactorily small.